Other snippets that have been accumulating over time suggest you are correct about the algorithm(s) being relatively simple. First hand accounts suggest they a

Other snippets that have been accumulating over time suggest you are correct about the algorithm(s) being relatively simple. First hand accounts suggest they are for the most part using simple linear regression; see this comment from a few years ago: https://news.ycombinator.com/item?id=19065226 https://news.ycombinator.com/item?id=19065226